The use of cyanide salts in copper plating electrolytes has become environmentally disfavored because of ecological considerations. Accordingly, a variety of non-cyanide electrolytes for various metals have heretofore been proposed for use as replacements for the well-known and conventional commercially employed cyanide counterparts. For example, U.S. Pat. No. 3,475,293 discloses the use of certain diphosphonates for electroplating divalent metal ions; U.S. Pat. Nos. 3,706,634 and 3,706,635 disclose the use of combinations of ethylene diamine tetra (methylene phosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, and aminotri (methylene phosphonic acid) as suitable complexing agents for the metal ions in the bath; U.S. Pat. No. 3,833,486 discloses the use of water soluble phosphonate chelating agents for metal ions in which the bath further contains at least one strong oxidizing agent; while U.S. Pat. No. 3,928,147 discloses the use of an organophosphorus chelating agent for pretreatment of zinc die castings prior to electroplating with electrolytes of the types disclosed in U.S. Pat. 3,475,293, 3,706,634 and 3,706,635.
While the eleotrolytes and processes disclosed in the aforementioned U.S. patents have provided satisfactory electrodeposits under carefully controlled conditions, such electrolytes and processes have not received widespread commercial acceptance in view of one or more problems associated with their practice. A primary problem associated with such prior art electrolytes has been inadequate adhesion of the copper deposit to zinc and zinc alloy substrates. Another such problem relates to the sensitivity of such electrolytes to the presence of contaminants such as cleaners, salts of nickel plating solutions, chromium plating solutions and zinc metal ions introduced into the electrolyte during conventional commercial practice. Still another problem is the hazardous nature of strong oxidizing agents employed in certain of such prior art electrolytes.
The present invention overcomes many of the problems and disadvantages associated with prior art cyanide-free copper plating solutions by providing an electrolyte which is cyanide-free providing an environmentally manageable system, which will function to produce an adherent copper deposit on conductive substrates including steel, brass and zinc base metals such as zinc die casts and the like; which will efficiently produce ductile, fine-grained copper deposits at thicknesses usually ranging from about 0.015 to about 5 mils (0.000015 to about 0.005 inch), which is more tolerant of the presence of reasonable concentrations of contaminants such as cleaning compounds, salts of nickel and chromium plating solutions and zinc metal ions as normally introduced into a plating bath in a commercial practice, and which is of efficient and economical operation.